1. Field
The invention relates to electronic digital tape timers and particularly to a simplified video tape timer employing a serial binary adder as a bi-directional counter, with associated timing and control arithmetic logic.
2. Prior Art
Electronic tape timers are employed to accurately locate a desired point along a tape during transport thereof by a suitable tape transport apparatus, while continuously indicating the amount of relative elapsed time that the tape has been moved. The indications of tape position may be a measure of elapsed time following the start of tape transport from a tape reference point, or of the time remaining before a reference point thereon is reached. Thus, a tape may be accurately stopped at a pre-selected frame as, for example, for editing purposes. It is desirable that the timer system provide accurate readout of the tape position at the tape transport location as well as several remote locations, for any of the standard multiple tape speeds and frame rates.
In a typical tape timer system, e.g., U.S. Pat. No. 3,573,360 to Rose et al., assigned to the same assignee as this application, a tape transport drives a tachometer device which supplies timing tach pulses to an electronic counter circuit. One tach pulse per second is generally obtained by employing suitable division ratios for each of the different tape speeds. The tach pulses are counted by the counter circuit, and eventually displayed by associated display apparatus in a time-of-day mode; i.e., in hours, minutes, seconds and/or tenths of seconds. As noted, the division ratios have to be adjusted to compensate for different tape speeds (e.g., four in the video magnetic tape transport art). Both the time-of-day counter circuit and the counters used for performing the division process have to count both up and down; in the first case to provide true real time operation in the event the transport is partially rewound, and in the second case to purge partial counts obtained if the transport is reversed after very brief runs, since the partial counts would add to straight-line operating time. In addition to the division by 8, 4, 2 or 1 to compensate for the four tape speeds (in a video tape recorder/reproducer), tighter time control when reversing count direction is desirable to reduce erroneous counts which might be obtained with tape direction reversals.
Thus, in a sophisticated video tape recorder/reproducer system, it is desirable that the associated time-of-day counter thereof provide; a counter each of whose digits counts moduli six and ten alternately; counting in moduli 8, 4, 2 and 1; generating a buffered count from the tachometer (for example, modulus ten herein); and the capability of changing the modulus of individual digits to display tenths of seconds as the least significant digit.